I'm sorry for multiple posting but I don't know what's the recommended way of proceeding in such circumstances. I think this is the same bug than bug # 476235, though the context is a little bit different (and bug # 476235 has been "resolved" two years ago!) so what I copy/paste below is a copy of what I have posted on https://bugzilla.mozilla.org/show_bug.cgi?id=476235 : ============================== I'm using Thunderbird 7.0.1 with Lightning 1.0b7 (and Google Agenda Provider 0.8) on Mac OS X 10.6.8. Here's how to reproduce it (you need to have already at least two calendars in your Lightning) : 1. Start Thunderbird 2. Go to Agenda 3. create a new event by double clicking on a day, leave all default options and juste save it 4. on the agendas list (or "calendars list" ?) located on the left pane, select one of your calendars by clicking on it (I personally have two calendars on my Thunderbird). 5. Click on the event you've just created on step 3 in order to select it. 6. Press the 'DEL' key on your keyboard. WARNING : press the 'DEL' key - NOT THE BACKSPACE KEY ! IMPORTANT - PLEASE NOTE : This bug only happens with the DEL key. The BACKSPACE key works fine and doesn't trigger this bug! Therefore, you'll need a full 104-keys USB keyboard in order to test it (the small wireless Apple Keyboard that comes with new Macs has no 'DEL' key on it but only a BACKSPACE key, but the combo Fn+Backspace should do the job, though not tested if it also triggers this bug this way or not). Also note : No need to select the multiweek or the month view : I tried all the 4 different views (day view, week view, etc.) and the bug remains exactly the same, whatever the current selected view is. ======================================= This bug must be quite recent because I'm a daily user of Thunderbird + Lightning and I guess I would definitively have seen this bug earlier if it were there for 2 years long. So this seems to be a regression.

Confirmed, sorry about that. Maybe you can find out since when this bug exists (i.e by installing older nightly builds)

Might be Mac OS X problem only. I was not able to reproduce on Windows 7.

vincent, can you reproduce this on linux or Mac?

I only use Linux, and I do not reproduce the problem.